I replaced the knobs on my JS with a set I bought at Radio Shack for about $2. They have set-screws in 'em so you can adjust them to whatever size pole piece. These knobs look just like the originals (which I still have) but they're extra-huge... I thought they looked kinda cool. Don't know if you have the shack in the UK though...
Also, sometimes knobs will not fit on the post of a potentiometer because the post ends (which are two split pieces of metal) have been squeezed together. Just stick a flathead screwdriver in them and pry them out a bit.
Oh, and the trem arm... I went around to music stores and asked about spare trem arms they have hanging around. No way they're gonna have a Jag Stang trem arm new in the box and probably not a mustang either. Anyway, they had some random trem arm that fit, just a little too long on the bridge end. No worries, just chopped off an inch or so with my dremel and viola! Fits like a glove and it cost me $5